Centralizers have been used for a long time for positioning a string in a subterranean location so that a sealing material such as cement can flow around it and can have a uniform thickness over the length of the cement job for greater sealing integrity between portions of a formation and the string passing through a borehole.
There have been a variety of techniques to centralize pipe including both structures added to the pipe and scoring and folding the pipe itself to form a centralizer as illustrated in U.S. Pat. No. 7,708,063. Usually, a pair of rings separated by bow springs is used and the structure is either slipped over the pipe on assembly of a string or is clamped to the pipe in the assembly process using end rings that are hinged so that they can be opened to mount to the pipe and then closed and secured over the pipe. Some examples are U.S. Pat. Nos. 4,641,776 and 4,531,582. Some designs were non-metallic sleeves that gave way when the string was internally expanded in the subterranean location such as U.S. Pat. No. 6,725,939. In other cases radially telescoping members were extended when the string was in the desired location to centralize the string as shown in U.S. Pat. No. 7,422,069. In U.S. Pat. No. 7,559,371 a centralizer was delivered through tubing and set itself in the casing below the tubing so that a central passage through the centralizer was aligned with a whipstock ramp. The milling string would pass through tubing and would be guided by the centralizer to stay on the whipstock ramp during window milling for a lateral. The centralizer was made of shape memory alloy and its reversion to an original shape allowed it to get a grip on a surrounding casing after passing through a narrower tubing string. In another design for a centralizer that accommodated expansion there were overlapping segments that had play so that the centralizer could grow with the internally expanded tubular, as shown in U.S. Pat. No. 7,624,798. Other older designs for centralizers are seen in U.S. Pat. Nos. 2,845,128; 2,849,071; 2,605,844 and 2,228,649. Rubber sleeves have been used in surface drilling equipment to centralize a drill string as shown in U.S. Pat. No. 4,182,424. Rubber or plastic sleeves with blades that are rigid enough to take the impacts during string delivery have been used as illustrated in U.S. Pat. Nos. 4,938,299; 7,159,668 and 5,908,072.
Centralizer present problems for the string being run in as parts of the centralizer can get hung up on shoulders or casing joints or landing collars. If pieces break off the centralizers the possibility exists that the string can get struck or that if the string is delivered successfully that the centralizers will not do their function of placement of the tubular for such operations as cementing or in the case of screens for gravel packing. It is therefore advantageous to have a centralizer that can change in dimension or volume as between run in and at full deployment of the string. The present invention envisions the use of such a design where the centralizer has a lower profile during run in and is then able to be configured when at location to serve as a tubular centralizer. In the preferred embodiment using a series of spaced shapes attached to the tubular outer wall and made from a shape memory alloy, polymer or foam. The material in its initial state is large enough to engage the wellbore wall when on location. Prior to mounting the material to the tubular it is heated above its transition temperature and compressed to a smaller shape and allowed to cool while compressed to retain the compressed shape. On location where the temperature is or is raised to above the transition temperature, the segments assume their original shape and volume so that the segments wind up in a supporting position for the tubular in a centralized manner. These and other aspects of the present invention will be more apparent to those skilled in the art by a review of the description of the preferred embodiment and associated drawings while understanding that the full scope of the invention is given by the appended claims.